1. Field of the Invention
The present invention relates to an optical disk drive, and more specifically, to an optical disk drive having a fixing structure with a fixed guide bar position to avoid deformation of the guide bar when being positioned in the optical disk drive.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a three-dimensional exploded view of a prior art optical disk drive. As shown in FIG. 1, the prior art optical disk drive comprises a main body 91, and a top shield 92 and a bottom shield 93 to enclose the main body 91. A tray 94 is installed inside the main body 91 for accommodating an optical disk (not shown), and the tray 94 extends and retracts from the front of the main body 91 (in the figure, the tray is retracted). A mounting plate 95 is installed in the main body 91. The mounting plate 95 comprises a spindle motor 96 for driving the rotation of the optical disk, and a pickup head 97 for reading/writing data on the optical disk. The pickup head 97 is guided by a guide bar 98 positioned on the mounting plate 95 to allow the pickup head 97 to move back and forth along a radial direction of the optical disk. In addition, the pickup head 97 reads/writes data on the optical disk with a laser beam emitted by the pickup head 97 by an optical means. Since the structure and the principle of this portion is similar to that of current optical disk drives, it is not mentioned further.
In consideration of the performance of an optical disk drive, to read/write data correctly is most important. Hence, whether or not the laser beam emitted by the pickup head 97 strikes on the surface of the optical disk at a correct angle is one of the key factors in reading/writing data correctly. As a result, all optical disk drive manufacturers calibrate the relative positions of the pickup head 97 and the rotation plane of the optical disk before optical disk drive products leave the factory to allow the laser beam generated by the pickup head 97 to reflect from the disk at the correct angle.
As to the calibration method, a very frequently utilized method is to keep the moving track of the pickup head 97 in a line, and to adjust the position of the rotation plane of the optical disk. When utilizing this method to calibrate the optical disk drive, the guide bar 98 is usually completely fixed on the mounting plate 95 so the moving track of the pickup head 97 mounted on and guided by the guide bar 98 will be kept along a lengthwise direction of the guide bar 98. An adjusting mechanism (not shown) is installed between the spindle motor 96 and the mounting plate 95 to fine tune the inclination angle between the spindle motor 96 and the plane in which the mounting plate 95 is located. Because the rotation of the optical disk is driven by the spindle motor 96, a slight change of the inclination angle of the spindle motor 96 will calibrate the relative positions of the rotation plane of the optical disk and the pickup head 97.
Please refer to FIG. 2. FIG. 2 is a partial exploded view of the optical disk drive depicted in FIG. 1 illustrating the assembly of a mounting plate and a guide bar. In order to illustrate more conveniently, the mounting plate 95 and the relevant parts in FIG. 1 are shown from a side opposite of that in FIG. 2. As shown in FIG. 2, a first end 981 and a second end 982 of the guide bar 98 of the prior art optical disk drive are fixed to the mounting plate 95 with a first fixed joint 991 and a second fixed joint 992, respectively. The first fixed joint 991 has a supporting part 9911 protruding from a surface of the mounting plate 95, and a fastening screw 9912 screwed to the mounting plate 95. The second fixed joint 992 has a base 961 for fixing the spindle motor 96, an indented engaging means 9921 on a surface of the base 961, and a stop block 9922 screwed to the base 961.
Please refer to FIG. 2, FIG. 3 and FIG. 4. FIG. 3 is a three-dimensional enlarged schematic diagram of portions of the optical disk drive depicted in FIG. 2 after being assembled illustrating the assembly of a first end of the guide bar and the mounting plate. FIG. 4 is a cross-sectional diagram along a line IV—IV in FIG. 3. As shown in FIG. 2 to FIG. 4, the first end 981 of the guide bar 98 is close to the surface of the mounting plate 95 and is positioned between the supporting part 9911 and the fastening screw 9912. The fastening screw 9912 has a head having a large diameter and a tapered inclined plane 9913 underneath the edge of the head. The further the fastening screw 9912 is screwed into the mounting plate 95, the larger the area of the tapering inclined plane 9913 contacting the surface of the first end 981 of the guide bar 98 to exert a pressing force to the first end 981. This pressing force will push the first end 981 to closely contact the mounting plate 95 and the supporting part 9911 so that the first end 981 is closely positioned between the supporting part 9911, the fastening screw 9912, and the mounting plate 95. An unmovable rigid fixing structure is thus formed.
Please refer to FIG. 5. FIG. 5 is a three-dimensional enlarged schematic diagram of portions of the optical disk drive depicted in FIG. 2 after being assembled illustrating the assembly of a second end of the guide bar and the mounting plate. As shown in FIG. 2 and FIG. 5, the second end 982 of the guide bar 98 is engaged with the engaging means 9921. Due to the existence of the stop block 9922 across the top of the engaging means 9921, the second end 982 in the engaging means 9921 is pressed so that the movements of the second end 982 towards both left and right are limited by the engaging means 9921, and the down movement of the second end 982 is hindered by the mounting plate 95. In addition, the upward movement of the second end 982 is suppressed by the stop block 9922. Therefore, an unmovable rigid fixing structure is formed.
However, the first end 981 and the second end 982 of the guide bar 98 are closely positioned on the mounting plate 95, rigidly and without freedom. Although the tightness of the positioning of the guide bar 98 is ensured, the accuracy of a flatness of the mounting plate 95 is not ensured when considering the practices used in manufacturing and assembly. When the previously mentioned rigidly fixing method is utilized to fix the guide bar 98 on the mounting plate 95, once the contact sites of the mounting plate 95 to the first end 981 and the second end 982 of the guide bar 98 are not in the same plane, the relative positions of the first end 981 and the second end 982 of the guide bar 98 will change with the non-planar mounting plate 95 because the first end 981 and the second end 982 are rigidly positioned on the mounting plate 95. Consequently, the guide bar 98 bends and deforms frequently. Furthermore, an automatic tool, such as an electrical screwdriver, is usually utilized when screwing the fastening screw 9912 or the stop block 9922 to the mounting plate 95. A torque generated by the automatic tool is considerable and can amplify the pressing force exerted on the first end 981 and the second end 982 of the guide bar 98, leading to a more severe bending and deformation of the guide bar. As a result, the moving track of the pickup head 97 guided by the guide bar 98 will not be in a line. Since the guide bar 98 loses its axial linearity, even though when there is a finely tuned design for the inclination angle between the spindle motor 96 and the mounting plate 95, it is impossible to ensure that the laser beam emitted by the pickup head 97 strikes on the surface of the optical disk at a correct angle at any site. The correctness and stability of reading/writing data on the optical disk by the pickup head 97 is seriously affected.
In another respect, once the guide bar 98 bends or deforms, the pickup head 97 will move back and forth on the guide bar 98 with uneven tension and relaxation. That means, when the pickup head 97 passes a deformed portion on the guide bar 98 having a large radius of curvature, a large torque is required from the motor of the transmission mechanism to drive the movement of the pickup head 97. Therefore, it is difficult for the servo control systems of the optical disk drive to control the movements of the pickup head 97 resulting in increased difficulty in assembly and complexity in calibration.